Design, performance and operation of the laser interferometric dilatometer

A dilatometer was designed and constructed to perform high precision thermal expansion measurements over the temperature range from ambient to 900 K. The design, construction, operation, and performance of the device is detailed. The measurement of length change employs an optical interferometer system which consists of a Michelson interferometer, a two frequency HeNe laser, and ac fringe detection. Length change precision of better than + or - 0.05 (SIGMA)m is achieved. Dilatometer control, status, data acquisition, and analysis functions are achieved by a minicomputer in order to achieve automated control. Further design features are incorporated which minimize sample preparation and assembly time to achieve rapid sample measurements. The interferometer alignment is under computer control to assist the operator during final adjustment and to maintain alignment throughout the course of a measurement. The performance of the device was evaluated by measurement of three thermal expansion standards (fused silica, platinum, and copper).